ILVerify: Handle readonly references in ldfld (#64077)

* ILVerify: Handle readonly references in ldfld

Fixes #63953

* Fix test name

Co-authored-by: Michal Strehovský <MichalStrehovsky@users.noreply.github.com>

Author: jkotas

src/coreclr/tools/ILVerification/ILImporter.Verify.cs

@@ -2060,7 +2060,7 @@ void ImportLoadField(int token, bool isStatic)
                     actualThis = StackValue.CreateByRef(actualThis.Type);
 
                 var declaredThis = owningType.IsValueType ?
-                    StackValue.CreateByRef(owningType) : StackValue.CreateObjRef(owningType);
+                    StackValue.CreateByRef(owningType, readOnly : true) : StackValue.CreateObjRef(owningType);
 
                 CheckIsAssignable(actualThis, declaredThis);
 

src/tests/ilverify/ILTests/ValueTypeTests.il

@@ -26,3 +26,16 @@
     }
 }
 
+.class public sequential ansi sealed beforefieldinit ValueTypeFieldTests
+       extends [System.Runtime]System.ValueType
+{
+    .field public int32 InstanceField
+
+    .method public static int32 ValueType.UnboxLdfld_Valid(object o) cil managed
+    {
+        ldarg.0
+        unbox      ValueTypeFieldTests
+        ldfld      int32 ValueTypeFieldTests::InstanceField
+        ret
+    }
+}